Vulnerability · Published Apr 7, 2026 · Assigned by GitHub_M
CVE-2026-39395Cosign's verify-blob-attestation reports false positive when payload parsing fails
Medium 4.3
In plain English
A medium-severity security flaw in cosign from sigstore. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Cosign provides code signing and transparency for containers and binaries. Prior to 3.0.6 and 2.6.3, cosign verify-blob-attestation may erroneously report a "Verified OK" result for attestations with malformed payloads or mismatched predicate types. For old-format bundles and detached signatures, this was due to a logic flaw in the error handling of the predicate type validation. For new-format bundles, the predicate type validation was bypassed completely. This vulnerability is fixed in 3.0.6 and 2.6.3.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | cosign | 2.6.3-r0 | ALPINE-CVE-2026-39395 |
| Alpine:v3.24 | cosign | 3.0.6-r0 | ALPINE-CVE-2026-39395 |
| Debian:13 | cosign | no fix listed | DEBIAN-CVE-2026-39395 |
| Debian:14 | cosign | 2.6.3-1 | DEBIAN-CVE-2026-39395 |
| Go | github.com/sigstore/cosign | 3.0.6 | GHSA-w6c6-c85g-mmv6 |
| Go | github.com/sigstore/cosign | no fix listed | GO-2026-5694 |
| Go | github.com/sigstore/cosign | 2.6.3 | GHSA-w6c6-c85g-mmv6 |
| Go | github.com/sigstore/cosign/v2 | 2.6.3 | GO-2026-5694 |
| Go | github.com/sigstore/cosign/v3 | 3.0.6 | GO-2026-5694 |
| Ubuntu:25.10 | cosign | no fix listed | UBUNTU-CVE-2026-39395 |
| Ubuntu:26.10 | cosign | no fix listed | UBUNTU-CVE-2026-39395 |
Affected products (as reported)
Weakness: CWE-754 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
References
- https://github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6 x_refsource_CONFIRM